Periodic Reporting for period 1 - MANACOLIPO (MAgnetoplasmonic NAnocavities for active COntrol of LIght POlarization)
Reporting period: 2022-08-01 to 2024-07-31
Enhancing magneto-optical (MO) effects is crucial for the size reduction of key photonic devices based on non-reciprocal propagation of light and for active nanophotonics, which can be one of the key building blocks for Internet-of-things (IoT) devices, lab-on-a-chip applications, quantum communication/computing, etc.
However, the achievable MO effect is still too small in sub-micron scale for practical applications.
Magnetoplasmonics merges the concepts from plasmonics and magneto-optics to achieve an enhancement of MO effects by typically using dipolar plasmonic resonances in ferromagnetic metal nanoantennas. The restrictions magnetoplasmonics currently faces are the low Q-factor of the dipolar plasmon resonances in magnetic metallic nanostructures, and their bright nature that enhances the radiation of light with the original incident polarization, thereby reducing the polarization change induced by the plasmon-assisted MO amplification.
This project has explored a new conceptual path: the hybridization of dipolar plasmon modes with multipolar dark modes using hybrid magnetoplasmonic nanocavities and a periodic arrangement to exploit surface lattice resonance to overcome the above-mentioned limitations.
However, the achievable MO effect is still too small in sub-micron scale for practical applications.
Magnetoplasmonics merges the concepts from plasmonics and magneto-optics to achieve an enhancement of MO effects by typically using dipolar plasmonic resonances in ferromagnetic metal nanoantennas. The restrictions magnetoplasmonics currently faces are the low Q-factor of the dipolar plasmon resonances in magnetic metallic nanostructures, and their bright nature that enhances the radiation of light with the original incident polarization, thereby reducing the polarization change induced by the plasmon-assisted MO amplification.
This project has explored a new conceptual path: the hybridization of dipolar plasmon modes with multipolar dark modes using hybrid magnetoplasmonic nanocavities and a periodic arrangement to exploit surface lattice resonance to overcome the above-mentioned limitations.
Work Performed
Optimization of the fabrication processes: We performed fabrication optimization for our magnetoplasmonics nanocavities, which requires e-beam lithography with sub-10 nm accuracy.
Design and characterization of various magnetoplasmonic nanocavity structures: We tested various nanocavity designs to see the dependence of the multipolar dark modes and their coupling with the dipolar bright modes.
Investigation of different materials for optimal nanocavity performance: We studied magnetic materials such as Permalloy (Fe₈₀Ni2₀) and Au/Co multilayers, aiming to optimize both their magnetic and plasmonic performances.
Optimization of array configurations to enhance MO effect: We investigated the functional arrangement of the magnetoplasmonic nanocavities to further enhance the MO effect with higher Q-factor.
Main Results Achieved
Gaining insights into the coupling between multipolar dark and dipolar bright modes in magnetoplasmonic nanocavities: We found that while the dipolar mode in the disk exhibits the strong bright resonance, the multipolar modes in the ring contribute to the suppression of the initial polarization with their dark nature and constructive interference with the disk dipole, further enhancing the MO effect.
Identification of Au/Co multilayers as a promising material due to its properties: When the thickness of Co in contact with Au is reduced to a few monolayers, it exhibits perpendicular magnetic anisotropy. The hybridization of Au with Co mitigates the intrinsic ohmic loss of Co, leading to enhanced plasmonic resonance in a disk structure. As a result, the Au/Co multilayer structure exhibits significantly greater magneto-optical enhancement compared to its film counterpart.
Successful enhancement of the MO effect through the exploitation of surface lattice resonances (SLR): The SLR is a Fano resonance that occurs between the resonance of individual nanocavities and the diffracted light resulting from their periodic arrangement. We studied various periodic configurations and demonstrated even greater MO enhancement, along with a higher Q factor, compared to nanodisks without SLR.
Optimization of the fabrication processes: We performed fabrication optimization for our magnetoplasmonics nanocavities, which requires e-beam lithography with sub-10 nm accuracy.
Design and characterization of various magnetoplasmonic nanocavity structures: We tested various nanocavity designs to see the dependence of the multipolar dark modes and their coupling with the dipolar bright modes.
Investigation of different materials for optimal nanocavity performance: We studied magnetic materials such as Permalloy (Fe₈₀Ni2₀) and Au/Co multilayers, aiming to optimize both their magnetic and plasmonic performances.
Optimization of array configurations to enhance MO effect: We investigated the functional arrangement of the magnetoplasmonic nanocavities to further enhance the MO effect with higher Q-factor.
Main Results Achieved
Gaining insights into the coupling between multipolar dark and dipolar bright modes in magnetoplasmonic nanocavities: We found that while the dipolar mode in the disk exhibits the strong bright resonance, the multipolar modes in the ring contribute to the suppression of the initial polarization with their dark nature and constructive interference with the disk dipole, further enhancing the MO effect.
Identification of Au/Co multilayers as a promising material due to its properties: When the thickness of Co in contact with Au is reduced to a few monolayers, it exhibits perpendicular magnetic anisotropy. The hybridization of Au with Co mitigates the intrinsic ohmic loss of Co, leading to enhanced plasmonic resonance in a disk structure. As a result, the Au/Co multilayer structure exhibits significantly greater magneto-optical enhancement compared to its film counterpart.
Successful enhancement of the MO effect through the exploitation of surface lattice resonances (SLR): The SLR is a Fano resonance that occurs between the resonance of individual nanocavities and the diffracted light resulting from their periodic arrangement. We studied various periodic configurations and demonstrated even greater MO enhancement, along with a higher Q factor, compared to nanodisks without SLR.
The new approaches and samples developed in this project will contribute to a deeper understanding of the nanoscale light-matter interactions. The demonstrated enhancement of the MO effect could lead to novel optical devices and components and applications in photonic nanotechnologies and active manipulation of light polarization.